Containers to be manufactured by blow molding or stretch blow molding are shaped from so-called preforms that have to be heated to a desired process temperature before the actual blowing procedure. To be able to reshape, during blow molding, the rotationally symmetric preforms, which normally have standardized wall thicknesses, to containers having a certain shape and wall thickness, individual wall regions of the preform must be subjected to dosed heating in a furnace, preferably with infrared radiation. To this end, usually a continuous stream of preforms is passed through a furnace with correspondingly adapted radiation sections. It is, however, a problem of such furnaces to selectively introduce a maximum proportion of the radiated thermal output into the preforms.
As an alternative, patent publication DE 10 2006 015853 A1 suggests to heat preforms in individual radiation chambers that each completely surrounds the preforms, the individual chambers being arranged like a carrousel. In the process, each preform is heated both by the inner wall of the chamber embodied as ceramic infrared radiator and by a rod-shaped infrared radiator which is introduced into the preform. In the process, the preform is essentially completely arranged within the radiation chamber.
DE 10 2006 015853 A1, however, says nothing as to how the loading of the furnace with preforms or the withdrawal of the same is to be designed in an efficient way to ensure an economical operation of the carousel furnace. However, just during the transfer at an infeed starwheel or a discharge starwheel, a problem arises in that a three-dimensional change of position of the preform must be accomplished within a very short time and with maximum transfer reliability, and in that the preforms must be placed sufficiently precisely in the individual heating chambers.
Therefore, there is a need for a furnace with separate heating chambers improved in this respect.